During operations performed to treat bone diseases of the spine, the surgeon fully or partially excises one or more vertebral bodies. The mechanical support previously given by this excised bone is therefore no longer provided. To overcome this disadvantage, rods are known to be used, generally titanium, and the spaces left empty after bone removal are filled with an inert, biocompatible material. A rod is inserted between two healthy vertebrae to provide initial support until injected cement material has hardened. An autologous single block graft, a bone from a bone bank or even a bone substitute may also be used.
Another technique consists of replacing the rod and biocompatible cement material by a rigid wired structure called a vertebral body, in which a bone graft is inserted to fill in the space left by bone removal and to provide a bony support. However to place the rigid cage in position it is necessary to draw aside adjacent vertebrae which leads to operative complications. In addition, the cage is opaque to X-rays.